A polymer electrolyte fuel cell is a device which causes a hydrogen-rich fuel gas and an oxidizing gas, such as air, containing oxygen to electrochemically react with each other to generate electric power and heat. To maintain ionic conductivity of polymer electrolytes (hydrogen ions) of a polymer electrolyte membrane used in the fuel cell, it is necessary to humidify and supply at least one of the fuel gas and the oxidizing gas (each of which is referred to as “reactant gas”). In a typical fuel cell system, a total enthalpy heat exchange type humidifying device humidifies the reactant gas by using as a heat source and a water source a highly-humidified off gas and discharged cooling water discharged from a stack.
Known as such humidifying device is a humidifying device configured by: stacking a steam permeable membrane and a separator which has on one of main surfaces a channel groove through which the reactant gas flows and on the other main surface a channel groove through which the discharged cooling water or the off gas flows; and fastening this stack body (see Patent Documents 1 and 2 for example).
The humidifying device disclosed in Patent Document 1 and 2 has the problem that at a portion of the separator which portion supports the steam permeable membrane, especially at a portion of the separator which portion is located between the channel grooves through which the reactant gas flows, the steam permeable membrane bends toward one of the separators by the difference of pressure between the reactant gas and the off gas, the expansion of the discharged cooling water caused due to freezing thereof, and the like, thereby being damaged. To be specific, in the case of the humidifying device which uses the reactant gas (secondary fluid) that is a humidified gas and the off gas (primary fluid) that is a humidifying gas, when the difference of pressure between the reactant gas and the off gas is large, the steam permeable membrane may bend toward a side where the pressure is low. Moreover, in the case of the humidifying device which uses the reactant gas (secondary fluid) as the humidified gas and the discharged cooling water (primary fluid) that is the humidifying fluid, the steam permeable membrane may bend toward the reactant gas side by the expansion of the discharged cooling water caused due to freezing thereof. Therefore, the problem is that a stress applied to the steam permeable membrane by a portion (convex portion) of the separator which portion supports the steam permeable membrane becomes different from a stress applied to the steam permeable membrane by a portion of the separator which portion is the channel groove (concave portion) through which the reactant gas or the discharged cooling water flows, and if these different stresses continue to be applied locally, the steam permeable membrane is damaged.
Since the steam permeable membrane is low in mechanical strength and easily damaged, proposed is a humidifier using a steam permeable membrane having high mechanical strength (see Patent Document 3 for example).
Moreover, to prevent the steam permeable membrane, which is low in mechanical strength, from being damaged, proposed is to provide a membrane guide member which has a mesh configuration or a large number of through holes and suppresses bending of the steam permeable membrane (see Patent Document 4 for example).
Patent Document 1: Japanese Laid-Open Patent Application Publication 9-7621
Patent Document 2: Japanese Laid-Open Patent Application Publication 2001-23662
Patent Document 3: Japanese Laid-Open Patent Application Publication 2000-348747
Patent Document 4: Japanese Laid-Open Patent Application Publication 2006-210150